1. Field of the Invention
The present invention relates to an electronic zoom apparatus used in a video camera, etc.
2. Description of the Related Art
In a video camera, etc. for transmitting information of a photographed image, the transmitted image information is converted to a digital signal through an analog/digital (which is briefly called A/D in the following description) converter. All the converted image data are written to a semiconductor memory. When the image data are read, only an image processed to be enlarged for example is selected. A calculating processing is then performed with respect to the selected image data to enlarge or reduce the size of the image stored to the semiconductor memory. The video camera, etc. are provided with a so-called electronic zoom apparatus having such a construction.
In such an electronic zoom apparatus, a contour portion of an image cannot be clearly displayed when an electronic zoom processing is performed. When a frequency for sampling an original image is set to high, there is a possibility that the contour portion of the image is displayed slightly clearly. However, when a zoom ratio is set to be large, the image contour portion cannot be displayed clearly.
When the above-mentioned sampling frequency is set to be high in consideration of the zoom ratio, the capacity of the above semiconductor memory becomes very large, which is not preferable in system construction.
There is a case in which an interpolation processing circuit is disposed to improve the quality of the electronic zoom-processed image mentioned above. In this case, when the interpolation processing is performed at the real time with respect to the image data A/D converted at a ratio 20 to 30 mega-sample/second (which is briefly called MSPS in the following description), it is necessary to perform the interpolation processing at a speed 34 to 50 nanoseconds. To execute such a calculating processing at a high speed, it is necessary to dispose a large-sized computer, etc. so that such a construction is not real. It is considered to use a digital signal processor (which is briefly called DSP in the following description), etc. Such a method has a general purpose, but has problems in consideration of operating time, etc. even when a pipeline processing is performed, and further becomes large-sized as a system.
As mentioned above, in the interpolating circuit, it is difficult to practically execute the interpolation processing of the image at the real time. Further, no interpolation processing is performed in many cases because of such problems.